Pilings which are formed from parent soil combined with a dry binder such as lime or cement. The diameter of the resulting piling can be varied from station to station to fulfill local structural requirements.
Stabilization of soil, and providing in-situ pilings with various physical properties that differ from their surroundings are known. The general technique is to bore into the soil, and while there, inject lime or cement, and sometimes water. The procedure mixes these materials together, and when they harden, they form a piling. The termxe2x80x9cpilingxe2x80x9d is used to denote a vertical rigid cylindrical structure, a body of revolution, having a strong vertical compressive strength, and often a lesser permeability compared to surrounding structure such as a clay soil.
These pilings have a longitudinal vertical axis, and a peripheral side wall that extends from the surface of the soil to the bottom of the piling. For convenience, its locations along the axis will be referred to asxe2x80x9cstationsxe2x80x9d, with station zero at the surface.
The formation of such pilings is known, for example in Ichise et al U.S. Pat. No. 3,802,203 and Mitani et al U.S. Pat. No. 4,606,675 the injection of cement into a surrounding formation while an augur is pressed into the earth is shown. These systems rely on the presence of existing water, and cement or lime is added to make an appropriate mixture that will harden to form the piling.
Applicant""s Gunther U.S. Pat. No. 5,967,700 performs the same function, but builds a piling constituted of a hardened stoichiometric mixture of the reactive ingredients. In particular this means adding the appropriate amount of water for the cement or lime from station to station.
In most of Europe, for example, usually there is enough water present to make at least a marginally effective piling. However this is not always the situation. For example in some areas around dams the soil is so dry that pits must be dug and water confined in them to soak the soil to the extent that a piling can ultimately be made, often many days later. The problem of dryness and variability of water content was solved by the said Gunther patent.
The established art enables cylindrical in-situ pilings to be formed to various degrees of certainty as to their properties. Especially the process defined in the Gunther patent can provide assurance that a stoichiometric mixture of water, lime and/or cement will be provided to assure the ultimate structural properties of the piling.
There remains, however, the limitation on all of the known processes that only a cylindrical piling is formed. This is not surprising, because the art of pilings has evolved from the driving of poles into the ground by percussive or vibration forces, or by drilling holes and later filling them with a material such as concrete, or as described above, mixing additives into a cylindrical structure to form an in-situ piling.
What is assumed in the established art is that a piling, even an in-situ piling that includes native soil in its composition will necessarily be consistent from top to bottom (which is the situation only with the said Gunther patent), and that its structural requirements will be the same from top to bottom.
To give assurance that the cylindrical shape will be adequate requires it to be over-designed for its location. This is because local conditions may vary from station to station. For example, an enlarged bulk might be needed near or at the lower end to anchor the piling in place or to take advantage of a very hard striation. To provident such a capacity there, the entire piling would have to be made as large.
Another example is the need for greater rigidity at some station where the surrounding earth is more fluid, or when an anchoring flange could usefully be formed to take advantage of a surrounding region of greater strength.
It is an object of this invention to provide a method to form a in-situ piling with a diameter which can selectively differ from station to station in a running manner so as to form a body of revolution with a structure suited to the requirement of localized regions in which it is generated.
This invention can utilize many types of apparatus to accomplish its objectives. The necessary requirements are apparatus such as a rotary augur or drill which will be rotated around its axis while it is being driven into the ground and withdrawn from it. Its function is to enable its own progress into the ground and to mix or stir the loosened soil as it goes in and out.
According to this invention, the device develops a column with a selectible diameter to create an in-situ piling of optimum cross-section, and even to form pilings of different diameters from station to station, using the same apparatus.
According to a preferred but optional feature of the invention, the apparatus can provide water in an amount to supplement the existing water so that their total volume is stoichiometrically related to the amount needed for the strength of the piling of cement, lime, or other dry binder that acts with water to develop a hard body. Dry binders composed of synthetic materials are known and are included in this invention. By xe2x80x9cdryxe2x80x9d is meant their condition when injected into the soil, where upon they meet the water to solidify the piling.